1. Field of the Invention
The present invention relates in general to automatic transmissions, and more particularly, to control systems for controlling the automotive automatic transmissions.
2. Description of the Prior art
In order to clarify the task of the present invention, one conventional control system for an automotive automatic transmission will be outlined, which is shown in Japanese Patent First Provisional Publication 59-62756.
The control system shown by the publication is so constructed as to judge the need for upshifting the transmission by analyzing information signals from an engine speed sensor and an engine load sensor. Upon judging the need, an electromagnetic means is operated to hydraulically control a gear change actuator to execute the upshift.
In the known control system, however, it sometimes occurs that, particularly in a higher engine load range, the upshift is not effectively made due to insufficiency in power performance of an associated engine.
That is, usually, in the higher engine load range, the gear change timing is set so as to achieve the upshift at a relatively low engine speed considering a considerable dispersion in engine speed during the gear change. As is known, the maximum engine speed during the gear change is forced to vary depending on dispersions in engine output torque, gear change hydraulic pressure and friction coefficients of various friction elements (viz., brakes, clutches and the like). In view of the unavoidable change in the maximum engine speed, the gear change timing for the upshift is set at such relatively low engine speed to prevent the engine speed from exceeding an allowable maximum speed.
Accordingly, even in case wherein a sufficient driving force is really needed at a higher speed range of the engine and a lower gear speed of the transmission, the upshift is forced to take plate at relatively early stage, which causes the transmission to fail to effectively use the engine performance.